nsIDOMNSHTMLDocument
inherits from: nsisupports last changed in gecko 6.0 (firefox 6.0 / thunderbird 6.0 / seamonkey 2.3) method overview void captureevents(in long eventflags); void clear(); boolean execcommand(in domstring commandid, in boolean doshowui, in domstring value); boolean execcommandshowhelp(in domstring commandid); obsolete since gecko 14.0 domstring getselection(); nsidomdocument open(in acstring acontenttype, in boolean areplace); boolean querycommandenabled(in domstring commandid); boolean querycommandindeterm(in domstring commandid); boolean querycommandstate(in domstring commandid); boolean querycommandsupported(in domstring...
... execcommandshowhelp() obsolete since gecko 14.0 (firefox 14.0 / thunderbird 14.0 / seamonkey 2.11) this method never did anything but throw an exception, and was removed entirely in gecko 14.0 (firefox 14.0 / thunderbird 14.0 / seamonkey 2.11).
... boolean execcommandshowhelp( in domstring commandid ); parameters commandid the name of the command.

Document - Web APIs
mozilla also define some non-standard methods: document.execcommandshowhelp()obsolete since gecko 14 this method never did anything and always threw an exception, so it was removed in gecko 14.0 (firefox 14.0 / thunderbird 14.0 / seamonkey 2.11).